All previous investigations have reported so large a percentage of "false abnormal" electrocardiographic (ECG) responses to exercise in women that the value of the ECG exercise test in women for the recognition of coronary insufficiency is seriously limited. However, the same ECG criteria were used for men and women, which is incorrect. It is proposed to determine the normal 95 percentile range limits of the ECG response to a standardized exercise test (progressive exercise on a treadmill up to 85% max VO2, predicted from the age-corrected heart rate). The upper (97.5%) and lower (2.5%) limits will be determined on the basis of the distribution of the various ECG items, particularly ST-T changes in a sample of 440 healthy women from 20 to 65 years. The effect of constitutional variables (age, body weight) and of arterial blood pressure will be considered in the statistical analysis of sex differences. A control group of 250 healthy men from 40 to 60 year will be investigated. On the basis of existent information, larger ST-T changes must be expected in women. In men, the value of the ECG exercise test for prediction of morbidity and mortality of coronary artery disease has been firmly established. It is expected that the sex-corrected standards resulting from this study will contribute to make the ECG exercise test as valuable in women as in men. In addition, it is proposed to compare the ECG responses to exercise in about 150 men and 50 women with similar degree of coronary heart disease, based on independent clinical information, including coronary arteriography. The purpose of this ancillary project is validation of the normal limits in clinical application, and to find out whether sex differences in the ECG response to exercise are maintained or abolished in presence of coronary artery disease.